1. Field of the Invention
This invention relates to a process for preparing high-detergency alkyl polyglycoside compositions and a purified alkyl monoglycoside and to compositions employing the alkyl polyglycosides for various end-use applications. In particular, the invention, involves removal or separation of a substantial portion of the alkyl monoglycoside present in a reaction product mixture containing alkyl polyglycosides resulting from the reaction of an alcohol and a saccharide at elevated temperatures in the presence of an acid catalyst.
2. Statement of Related Art
The reaction of a reducing saccharide, e.g. an aldose or ketose saccharide, or a source thereof, with an alcohol results in the formation of a glycoside. Acids catalyze the reaction between a reducing saccharide and an alcohol. When the alcohol is an alkanol, the resulting glycoside is commonly referred to as an alkyl glycoside. Alkyl glycosides are structurally stable to alkali. Long chain, higher, alkyl (C.sub.8-18) groups contribute to surface activity, e.g. detergency, of the glycoside. Thus, long chain alkyl monoglycosides and mixtures thereof with long chain alkyl polyglycosides are known materials, are known to be surface active in character and are known to be useful in a wide variety of household and industrial applications. It is also known that glycoside surfactants can be prepared by reacting a long chain alcohol with a saccharide reactant (e.g., a monosaccharide or a material hydrolyzable to a monosaccharide) at an elevated temperature in the presence of an acid catalyst. U.S. Pat. 4,987,225 contains an extensive listing of processes for preparing alkyl glycoside compositions. As disclosed therein, processes for preparing alkyl glycoside compositions are disclosed in U.S. Pat. No. 3,219,656 to Boettner (issued Nov. 23, 1965); U.S. Pat. No. 3,547,828 to Mansfield et al. (issued Dec. 15, 1970); U.S. Pat. No. 3,598,865 to Lew (issued Aug. 10, 1971); U.S. Pat. No. 3,707,535 to Lew (issued Dec. 26, 1972); U.S. Pat. No. 3,772,269 to Lew (issued Nov. 13, 1973); U.S. Pat. No. 3,839,318 to Mansfield (issued Oct. 1, 1974); U.S. Pat. No. 4,349,669 to Klahr (issued Sep. 14, 1982); U.S. Pat. No. 4,393,203 to Mao et al. (issued Jul. 12, 1983); U.S. Pat. No. 4,472,170 to Hellyer (issued Sep. 18, 1984); U.S. Pat. No. 4,483,979 to Mao (issued Nov. 20, 1984); U.S. Pat. No. 4,510,306 to Langdon (issued Apr. 9, 1985); U.S. Pat. No. 4,597,770 to Forand et al. (issued Jul. 1, 1986); U.S. Pat. No. 4,704,453 to Lorenz et al. (issued Nov. 3, 1987); U.S. Pat. No. 4,713,447 to Letton (issued Dec. 15, 1987); published European Application No. 83302002.7 (EPO Publication No. 0092355; Vander Burgh et al; published Oct. 26, 1983); published European Application No. 83200771.0 (EPO Publication No. 0096917; Farris; published Dec. 28, 1983); and published European Application No. 84303874.6 (EPO Publication 0132043; published Jan. 23, 1985).
During the course of the aforementioned acid-catalyzed saccharide reactant/long chain alcohol reaction process there is usually employed a substantial stoichiometric excess of the long chain alcohol reactant. The resulting reaction product mixture as initially made (i.e., without any intervening separation, fractionation or purification operations) typically contains a substantial molar excess of residual unreacted long chain alcohol, the monoglycoside of the long chain alcohol as the predominant glycoside molecular species both a mole and weight percentage bases, and the various higher degree of polymerization long chain alcohol polyglycoside species in progressively decreasing percentage amounts or proportions .
In accordance with the various prior art references, it has been conventional practice to remove the residual unreacted long chain alcohol from the indicated reaction mixture via various techniques such as vacuum distillation, organic solvent (e.g. acetone) extraction or fractionation, and thin (or wiped) film evaporation.
Several methods of removal of the alcohols from the crude alkyl polyglycoside reaction product have been proposed. In Japanese Application No. 63-256398, laid open Apr. 16, 1990, No. 02-103202, a method of removing the alcohol by supercritical gas extraction, more specifically carbon dioxide, is described. In German Application DE 3932173, a two-stage distillation separation of alcohol from the mixture of alkyl glycosides is described using a falling film evaporator and thin film evaporator. Another distillation separation of alkyl glycosides and alcohol is described in U.S. Pat. No. 4,889,925 in which a viscosity-reducing agent is added to the alcohol-glycoside reaction mixture, which is then distilled at a temperature up to about 160.degree. C. at a pressure of about 1 to 10.sup.-3 mbar.
If the long chain (fatty) alcohol is removed from the reaction mixture by one of the distillation or evaporation methods, the polysaccharide by-products and any other materials with low volatility remain in the alkyl glycoside product. Thus, in each of the methods described above the intent is to remove the alcohol leaving behind the alkyl glycosides, including the alkyl monoglycoside. The product will contain the monoglycoside of the long chain alcohol as the predominant glycoside species on a percentage basis and various higher degree of polymerization long chain alcohol polyglycoside species in progressively decreasing mole percentage amounts or proportions from the DP2 through DP10 and higher glycosides.